OBJECTIVE To determine the incidence, duration, and genetic diversity of colonization with vancomycin-resistant Enterococcus faecium (VREF). METHODS Oncology unit of a 650-bed university hospital. METHODS Surveillance perianal swab cultures were performed on admission and weekly. The molecular relatedness of VREF isolates was determined by pulsed-field gel electrophoresis and by the hybridization pattern of the vanA resistance determinant. RESULTS During 8 months of surveillance, the VREF colonization rate was 16.6 patients per 1,000 patient-hospital days, which was 10.6 times greater than the VREF infection rate. Eighty-six patients with VREF colonization were identified. Colonization persisted for at least 7 weeks in the majority of patients. Of 36 colonized patients discharged from the hospital and then readmitted, an average of 2 1/2 weeks later, 22 (61%) patients still were colonized with VREF. Of the 14 patients who were VREF-negative at readmission, only three patients remained culture-negative throughout hospitalizations. PFGE demonstrated that colonization with the same VREF isolate may persist for at least 1 year, and patients may be colonized with more than one strain of VREF. CONCLUSIONS VREF colonization is at least 10-fold more prevalent than infection among oncology patients. Colonization often persists throughout lengthy hospitalizations and may continue for long periods following hospitalization.